1. Field of the Invention
The present invention relates to methods of making diamond powder, and doped diamonds from a hydrocarbon and fluorocarbon mixture.
2. Background of the Invention
Thermal decomposition of solid hydrocarbons of different molecular structure and types of carbon bonding under a pressure (P) of 8 GPa and temperature (T) of 1500° C. are known. It has been shown that heating naphthalene under such conditions, causes its chemical decomposition into a carbon residue and volatile gases. Depending on the heating temperature and duration of heating, (time (t) the carbon residue crystallizes in different crystal forms. When heated for 1 min, the carbon residue crystallizes in a mixture of: two-dimensionally ordered carbon (at T=500-600° C.), three-dimensionally ordered carbon (such as graphite with an interplanar distance (d002) from 0.3440 nm at T=700° C. to 0.3354 nm at T=1150° C.), and complete conversion to diamond at T=1300° C. It has also been observed that when graphite is in contact with naphthalene at an internal surface of a graphite boat heater, it transforms into diamond at a pressure of 8 GPa and a temperature of 1300° C.
Experimentation with naphthalene to yield diamond from graphite, helped elucidate that along with pressure, temperature and time, the concentration (c) of chemically bonded hydrogen (in the graphite reaction zone of the high pressure apparatus), is important. Such concentrations can be varied by changing the ratio (a/b) of components in finely dispersed mixtures of graphite and naphthalene (C10H8):αCgraphite+b C10H8 naphthalene  (1)
It is known that when the concentration of bonded hydrogen is equal or higher than 1% of the total mass of the mixture (i.e., mass ratio of graphite and naphthalene in the homogeneous mixture is 5.25:1), all the carbon residue of the mixture (1) converts into diamond under conditions where:P=8 GPa, T=1300° C., and t=20 sec  (2)
Thermobaric treatment of mixtures of graphite and naphthalene at a concentration below 1 wt. % causes a drop in the yield of diamond, so that at (c)≦0.3% (i.e., at mass ratio of graphite to naphthalene about 20:1) virtually no diamond is formed under the experimental parameters (2). Research by Bundy F. P. entitled “Direct conversion of graphite to diamond in static pressure apparatus” (J. Chem. Phys. 1963, V. 38, N 3, pp. 631-643); as well as that of Vereschagin L. F. et al. entitled “Direct transformation of graphite into diamond under high static pressures,” (Doklady AN SSSR. 1972, V. 206, N1, pp. 78-79), show that direct (catalyst-free) transformation of graphite into diamond requires pressures above 12 GPa and at temperatures of about 3000° C. Such high pressure and high temperature ranges makes the commercial synthesis of such material technically difficult.
The fact that the reaction temperature for the formation of diamond from hydrocarbon is significantly lower than the temperature required for the direct transformation of graphite into diamond can be explained; as the activation energy required for thermal destruction of hydrocarbon is much lower than graphite, which possesses a highly ordered crystalline frame which is resistant to thermal treatment. The finding that the introduction of chemically bonded hydrogen (naphthalene, C10H8), into the reaction zone filled with graphite (which gives an overall hydrogen-to-carbon atomic ratio of 1:8) causes a reduction in temperature, pressure and time required for the transformation of graphite into diamond is of interest. However the mechanism by which hydrogen influences the synthesis of diamond from graphite is unknown, also the form of hydrogen that participates in the process of diamond formation is unknown and may be atomic or molecular hydrogen, volatile gaseous hydrocarbons, or any combination thereof.
Indirect evidence about the process taking place in the high pressure chamber (HPC) under a high pressure and high temperature (HPHT) has been obtained based upon studies of samples which are isolated after the end of experimentation, that is after the pressure and temperature have been quenched to ambient conditions. However the process of cooling and pressure release may also induce changes, in addition to the transformations which took place under HPHT.
One such indirect observation is that on heating of naphthalene for about 10 seconds at temperature of 600° C. under a pressure of 8 GPa, followed by cooling and lowering the pressure to atmospheric, the reaction product isolated from the HPC is a two-dimensional ordered carbon having a hydrogen content of about 1 wt. % and showing a weight loss of about 24% relative to the starting mass of naphthalene. This weight loss suggests that hydrogen is being removed from the sample, most likely in the form of methane CH4, (although the formation of mixtures of hydrogen and other gaseous hydrocarbons during the decomposition process of naphthalene cannot be excluded).
It therefore seems likely that the gaseous hydrocarbon products of degradation of naphthalene partially remain in the reaction zone up to temperature of 1300° C. and facilitate the formation of diamond from graphite when a pressure of 8 GPa, and a temperature of 1300° C. is reached and maintained for 20 seconds. It is believed therefore, that hydrogen or hydrocarbon gas can participate in the transformation of graphite into diamond, either through deformation of the crystalline frame of graphite by intercalation or by chemical splitting, followed by chemical transport of carbon.
In view of the above cited limitations of conventional methods for diamond synthesis, there is a clear need for a method of producing diamonds that is clearly understood and more efficient than conventional methods. For example, catalysts for diamond synthesis conventionally are metal systems which are used to dissolve the carbon and accelerate conversion of graphite/carbon source to diamond, however such solvent-catalyst systems, result in metal impurities within the diamond lattice structures. Therefore a low temperature, catalyst free method to produce highly pure nano and micron-size diamond powder and doped diamond crystals that requires a significantly lower reaction temperature compared to conventional methods would be particularly well received.